Abstract: The aim of this paper is to study the effect of temperature on cleavage fracture toughness of weld thermal simulated X80 pipeline steels in ductile-to-brittle transition (DBT) regime. A large number of fracture toughness (as denoted by crack tip opening displacement-CTOD) tests together with finite element analyses are carried out by using deep-cracked single edge notched bending (SENB with a/W=0.5) specimens at various temperatures (-90℃, -60℃, -30℃ and 0℃). 3D finite element models of tested specimens have been used for the numerical simulation in this study. Coarse-grained heat-affected zone (CGHAZ) is considered as the material microstructure in preparation of weld thermal simulated fracture mechanics specimens. It has been found that the transferability of the true stress-strain curves obtained from weld thermal simulated round tensile bar to the fracture mechanics specimens works very well. Temperature shows only a slight effect on the material hardening behavior. As compared with experimental results, the 3D model can precisely predict the fracture toughness (CTOD-values) at different temperatures considered in this study.